Automated test equipment is used to perform a wide variety of tests that might otherwise be performed manually at a slower rate and/or greater cost. Automation of a test typically involves the reading of measurements from a device under test from which calculations are performed to determine whether the device under test is within or outside of acceptable test limits. For example, in the large-scale production of electronic circuits, automated test equipment is used for performing tests on each circuit board of a run of circuit boards. A run is a testing sequence of the same type of assembly with no intervening different types of assemblies. A typical automated circuit tester includes a test configuration circuit, a bed-of-nails fixture, and a set of programmable relay matrices and internal measurement busses. A circuit under test is positioned on the bed-of-nails fixture such that the nails electrically connect to nodes of the circuit under test. The measurement paths from the circuit under test to the test configuration circuit are connected by programming the appropriate relays in that path to close. While the relays in the measurement path are closing, the test configuration circuit is set up and prepared to take actual measurements. After the relays have closed, measurements are read from the circuit under test. Calculations are performed based on the measurements to determine whether the circuit under test passed the test.
In the prior art, automated testers obtain each required measurement in real-time-that is, each measurement that is required in the calculations that determine whether the test passed or failed are physically acquired on each test of a device under test that is part of the same test run. In many applications, however, several of the required measurements do not change significantly over time. This may be due to system-level error sources that generally remain constant for a particular test run. The taking of these stable error source measurements results in unnecessary test time overhead. Accordingly, a need exists for a method for reducing the number of real-time test measurements over a run of devices under test.